Hydrostatic seal with aft tooth

ABSTRACT

A hydrostatic seal configured to be disposed between relatively rotatable components. The seal includes a base. The seal also includes a seal housing. The seal further includes a shoe operatively coupled to the base and extending axially from a forward end to an aft end. The seal yet further includes a plurality of teeth extending radially from a sealing surface of the shoe, one of the teeth being a longest tooth that extends furthest radially from the sealing surface, the axial distance from the forward end of the shoe to the longest tooth being greater than a radial distance from a radial tooth tip to the sealing surface.

BACKGROUND

Exemplary embodiments pertain to the art of gas turbine engines and,more particularly, to a hydrostatic seal having an aft tooth.

Hydrostatic seals exhibit less leakage compared to traditional knifeedge seals while exhibiting a longer life than brush seals. Somehydrostatic seals may be used between a stator and a rotor within a gasturbine engine. The hydrostatic seal is mounted to the stator tomaintain a desired gap dimension between the hydrostatic seal and therotor. The hydrostatic seal has the ability to ‘track’ the relativemovement between the stator and the rotor throughout the engineoperating profile when a pressure differential is developed across theseal.

Hydrostatic seals involve motion of a spring-attached shoe whoseresponse is based on aerodynamic forces developed between the seal shoeand a rotor surface during operation. When properly designed, thehydrostatic seal will maintain tight clearances across the operatingrange of the engine. At tight clearances, the flow under the seal shoeacts as a high-speed jet whose behavior can exhibit variability that canresult in negative performance of the seal. In addition, for seals oflonger axial length, the pressure variations downstream of the primarypack of seal teeth can result in undesirable aero-mechanical propertiesof the seal for a given mode.

BRIEF DESCRIPTION

Disclosed is a hydrostatic seal configured to be disposed betweenrelatively rotatable components. The seal includes a base. The seal alsoincludes a seal housing. The seal further includes a shoe operativelycoupled to the base and extending axially from a forward end to an aftend. The seal yet further includes a plurality of teeth extendingradially from a sealing surface of the shoe, one of the teeth being alongest tooth that extends furthest radially from the sealing surface,the axial distance from the forward end of the shoe to the longest toothbeing greater than a radial distance from a radial tooth tip to thesealing surface.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth islocated at the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality of teethincludes a cluster of teeth and the aft tooth, each of the cluster ofteeth located closer to the forward end than to the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth isaxially spaced from the cluster of teeth, the axial spacing of the afttooth from the cluster of teeth being greater than 50% of the axiallength of a sealing surface of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include a beam operatively couplingthe shoe to the base.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the beam is one of aplurality of beams oriented parallel to each other.

Also disclosed is a seal assembly disposed in a gas turbine engine. Theseal assembly includes a first component. The seal assembly alsoincludes a second component, the first component and the secondcomponent relatively rotatable components. The seal assembly furtherincludes a first hydrostatic seal disposed between the first componentand the second component. The seal includes a base. The seal alsoincludes a shoe operatively coupled to the base and extending axiallyfrom a forward end to an aft end to define an axial length. The sealfurther includes a plurality of teeth extending radially from a sealingsurface of the shoe, one of the teeth being an aft tooth located closerto the aft end than to the forward end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth islocated at the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality of teethincludes a cluster of teeth and the aft tooth, each of the cluster ofteeth located closer to the forward end than to the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth isaxially spaced from the cluster of teeth, the axial spacing of the afttooth from the cluster of teeth being greater than 50% of the axiallength of a sealing surface of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include a beam operatively couplingthe shoe to the base.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the beam is one of aplurality of beams oriented parallel to each other.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first component isa stator and the second component is a rotor.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the seal isoperatively coupled to the stator.

Further disclosed is a gas turbine engine including a compressorsection, a combustor section, a turbine section, and a seal assemblydisposed in the gas turbine engine, the seal assembly comprising astator, a rotor, and a first hydrostatic seal disposed between a statorand the rotor. The seal includes a base. The seal also includes a shoeoperatively coupled to the base and extending axially from a forward endto an aft end to define an axial length. The seal further includes aplurality of teeth extending radially from a sealing surface of theshoe, one of the teeth being an aft tooth located closer to the aft endthan to the forward end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth islocated at the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality of teethincludes a cluster of teeth and the aft tooth, each of the cluster ofteeth located closer to the forward end than to the aft end of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the aft tooth isaxially spaced from the cluster of teeth, the axial spacing of the afttooth from the cluster of teeth being greater than 50% of the axiallength of a sealing surface of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include a beam operatively couplingthe shoe to the base.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a side, partial cross-sectional view of a gas turbine engine;

FIG. 2 is a perspective view of a portion of a hydrostatic sealassembly;

FIG. 3 is cross-sectional view of the hydrostatic seal assemblyaccording to an aspect of the disclosure;

FIG. 4 is a cross-sectional view of a shoe of the hydrostatic sealaccording to an aspect of the disclosure; and

FIG. 5 is a cross-sectional view of the shoe of the hydrostatic sealaccording to an aspect of the disclosure.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct, while the compressorsection 24 drives air along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a two-spool turbofan gasturbine engine in the disclosed non-limiting embodiment, it should beunderstood that the concepts described herein are not limited to usewith two-spool turbofans as the teachings may be applied to other typesof turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through aspeed change mechanism, which in exemplary gas turbine engine 20 isillustrated as a geared architecture 48 to drive the fan 42 at a lowerspeed than the low speed spool 30. The high speed spool 32 includes anouter shaft 50 that interconnects a high pressure compressor 52 and highpressure turbine 54. A combustor 56 is arranged in exemplary gas turbine20 between the high pressure compressor 52 and the high pressure turbine54. An engine static structure 36 is arranged generally between the highpressure turbine 54 and the low pressure turbine 46. The engine staticstructure 36 further supports bearing systems 38 in the turbine section28. The inner shaft 40 and the outer shaft 50 are concentric and rotatevia bearing systems 38 about the engine central longitudinal axis Awhich is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion. It will be appreciated that each of the positions of the fansection 22, compressor section 24, combustor section 26, turbine section28, and fan drive gear system 48 may be varied. For example, gear system48 may be located aft of combustor section 26 or even aft of turbinesection 28, and fan section 22 may be positioned forward or aft of thelocation of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present disclosure isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,688 meters). The flight condition of 0.8 Mach and35,000 feet (10,688 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Lowcorrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second (350.5 m/sec).

FIGS. 2 and 3 illustrate a hydrostatic seal indicated generally at 100.The hydrostatic seal 100 is intended to create a seal between tworelatively rotating components, such as a fixed stator and a rotatingrotor 102. The hydrostatic seal 100 includes a base portion 107 and atleast one, but often a plurality of circumferentially adjacent shoes 108which are located in a non-contact position along the exterior surfaceof the rotor 102. Each shoe 108 is formed with a sealing surface 110.For purposes of the present disclosure, the term “axial” or “axiallyspaced” refers to a direction along the rotational axis of the rotor,whereas “radial” refers to a direction perpendicular to the rotationalaxis of the rotor. FIG. 3 illustrates axial direction X and radialdirection Z.

Under some operating conditions, it is desirable to limit the extent ofradial movement of the shoes 108 with respect to the rotor 102 tomaintain tolerances, such as the spacing between the shoes 108 and thefacing surface of the rotor. The hydrostatic seal 100 includes at leastone spring element 114. In the current embodiment, each spring element114 is formed with at least one beam though in practice other elementscould be utilized to create the spring element. In the illustratedembodiment, two beams are shown, specifically an inner beam 116 a and anouter beam 116 b. The beams 116 a, 116 b connect the shoe 108 to thebase portion 107 of the seal 100. The base portion 107 is fixed to acarrier 120 that is part of a static structure.

Particularly when the hydrostatic seal 100 is used in applications suchas gas turbine engines, pressures are developed which apply anaerodynamic forces to the shoe 108, which is counter-balanced by thespring 114, causing it to move radially with respect to the rotor 102.The initial assembly point has a defined radial gap between the shoe 108and the rotating surface, with no aerodynamic forces acting upon theshoe 108. In operation, the hydrostatic seal 100 is used to restrictflow between a high pressure region H and a lower pressure region L. Toassist with the flow restriction, a plurality of teeth 118 are includedon the sealing surface 110 of the shoe 108. The pressure drop across theshoe 108 results in a radial force R on the shoe 108 which is counterbalanced by the spring 114 with spring force S. In operation, when theair flow between the shoe 108 and rotor 102 increases, the pressures onthe shoe 108 generally decrease. The reduction in pressures along theshoe 108 reduces the radial force acting on the shoe 108 such that theforce balance between the overall aerodynamic forces on the seal shoeand the spring force S causes the shoe 108 to be pushed radiallyinwardly toward the rotor 102, thus decreasing the gap, until the sealreaches an equilibrium position considering the spring force of thedisplaced beam(s). Conversely, in operation, when the air flow betweenthe shoe 108 and rotor 102 decreases, the pressures on the shoe 108generally increase. The increase of radial force on the shoe 108, andits overall impact with the net aerodynamic forces on the seal shoe 108considering the spring force S, causes the shoe 108 to move radiallyoutwardly from the rotor 102 until the seal reaches an equilibriumposition considering the spring force of the displaced beam(s).

Energy from adjacent mechanical or aerodynamic excitation sources (e.g.rotor imbalance, flow through the seal, other sections of the engine,etc.) may be transmitted to the seal 100, potentially creating avibratory response in the seal 100. For a seal with undesirableaero-mechanical properties, the vibratory response of the shoes 108 attheir natural frequencies can be self-reinforcing, causing unwantedvibration levels and possible deflection of the shoes 108. Suchvibratory responses create vibratory stress leading to possible reducedlife of the seal 100, and can be large enough to cause unintendeddeflections of the shoes 108.

As shown in FIGS. 2-5, the sealing surface 110 of the shoe 108 includesthe plurality of teeth 118 projecting therefrom. In typical toothconfigurations, a cluster of teeth are positioned together proximate aforward end 122 of the shoe 108. The shoe 108 extends axially from theforward end 122 to an aft end 124 to define an axial length of the shoe108. In the typical tooth configurations—with all teeth locatedproximate the forward axial half of the shoe 108—the radial spacebetween the rotor 102 and the sealing surface 110 of the shoe 108operates as what may be characterized as a diffuser at an axial spacedefined by the most aft tooth of the teeth cluster and the exit area ofthe flow. The geometry of the diffuser changes as the seal gap changesfrom a build clearance to a smaller running clearance. On a diffusermap, this can result in diffuser aerodynamic flow changing fromrelatively stable fluid dynamics to maximum aerodynamic unsteadiness.

In the embodiments disclosed herein, one or more teeth are positioned inthe conventional forward location, but an aft tooth 118 a is alsoprovided to be located proximate the aft end 124 of the shoe 108 tostabilize the flow between the rotor 102 and the shoe 108 by improvingthe seal pressure characteristics on the downstream portion of the shoe108. The aft tooth 118 a is the tooth of the plurality of teeth 118located axially closest to the aft end 124 of the shoe 108. Althougheach of the illustrated embodiments depict the aft tooth 118 a beinglocated precisely at the aft end 124 of the shoe 108, it is to beunderstood that the location of the aft tooth 118 a “proximate the aftend 124” is defined by locations at the aft end 124 in some embodimentsand spaced axially forward from the aft end 124 in other embodiments.For embodiments with the aft tooth 118 a spaced axially forward from theaft end 124, the aft tooth 118 a must be axially located at an axiallyaft half of the shoe 108. Specifically, the axial length mid-point ofthe shoe 108 is located at an axial location that is 50% of the axiallength of the shoe 108. The aft tooth 118 a is located axially rearwardof the axial length mid-point. In other words, the aft tooth 118 a islocated closer to the aft end 124 of the shoe 108 than to the forwardend 122 of the shoe 108.

As shown in FIGS. 4 and 5, the number of teeth considered to be part ofthe forward cluster of teeth referred to with numeral 118 may vary.Additionally, the radial lengths of the teeth and axial spacingtherebetween may vary depending upon the particular application.Regardless of the number, dimensions and geometric orientation of theteeth 118, the above-described aft tooth 118 a is axially spaceddownstream therefrom to effectively eliminate the diffusercharacteristics that are present with prior seal designs. The axialspacing of the aft tooth 118 a from the cluster of teeth 118 is greaterthan 50% of the axial length of the sealing surface 110 of the shoe 108.The lifting force balance is changed as the controlling area moves torear of the seal shoe 108, but large scale dynamic unsteadiness underthe shoe 108 is reduced or eliminated.

The embodiments described herein improve the sealing performancerobustness of the seal 100 via improved damping characteristics and flowjet stabilization at certain conditions.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A hydrostatic seal configured to be disposedbetween relatively rotatable components, the seal comprising: a base; ashoe operatively coupled to the base and extending axially from aforward end to an aft end to define an axial length; and a plurality ofteeth extending radially from a sealing surface of the shoe, one of theteeth being an aft tooth located closer to the aft end than to theforward end of the shoe.
 2. The seal of claim 1, wherein the aft toothis located at the aft end of the shoe.
 3. The seal of claim 1, whereinthe plurality of teeth includes a cluster of teeth and the aft tooth,each of the cluster of teeth located closer to the forward end than tothe aft end of the shoe.
 4. The seal of claim 3, wherein the aft toothis axially spaced from the cluster of teeth, the axial spacing of theaft tooth from the cluster of teeth being greater than 50% of the axiallength of a sealing surface of the shoe.
 5. The seal of claim 1, furthercomprising a beam operatively coupling the shoe to the base.
 6. The sealof claim 5, wherein the beam is one of a plurality of beams orientedparallel to each other.
 7. A seal assembly disposed in a gas turbineengine, the seal assembly comprising: a first component; a secondcomponent, the first component and the second component relativelyrotatable components; and a first hydrostatic seal disposed between thefirst component and the second component, the seal comprising: a base; ashoe operatively coupled to the base and extending axially from aforward end to an aft end to define an axial length; and a plurality ofteeth extending radially from a sealing surface of the shoe, one of theteeth being an aft tooth located closer to the aft end than to theforward end of the shoe.
 8. The seal assembly of claim 7, wherein theaft tooth is located at the aft end of the shoe.
 9. The seal assembly ofclaim 7, wherein the plurality of teeth includes a cluster of teeth andthe aft tooth, each of the cluster of teeth located closer to theforward end than to the aft end of the shoe.
 10. The seal assembly ofclaim 9, wherein the aft tooth is axially spaced from the cluster ofteeth, the axial spacing of the aft tooth from the cluster of teethbeing greater than 50% of the axial length of a sealing surface of theshoe.
 11. The seal assembly of claim 7, further comprising a beamoperatively coupling the shoe to the base.
 12. The seal assembly ofclaim 11, wherein the beam is one of a plurality of beams orientedparallel to each other.
 13. The seal assembly of claim 7, wherein thefirst component is a stator and the second component is a rotor.
 14. Theseal assembly of claim 13, wherein the seal is operatively coupled tothe stator.
 15. A gas turbine engine comprising: a compressor section; acombustor section; a turbine section; and a seal assembly disposed inthe gas turbine engine, the seal assembly comprising a stator, a rotor,and a first hydrostatic seal disposed between a stator and the rotor,the seal comprising: a base; a shoe operatively coupled to the base andextending axially from a forward end to an aft end to define an axiallength; and a plurality of teeth extending radially from a sealingsurface of the shoe, one of the teeth being an aft tooth located closerto the aft end than to the forward end of the shoe.
 16. The gas turbineengine of claim 15, wherein the aft tooth is located at the aft end ofthe shoe.
 17. The gas turbine engine of claim 15, wherein the pluralityof teeth includes a cluster of teeth and the aft tooth, each of thecluster of teeth located closer to the forward end than to the aft endof the shoe.
 18. The gas turbine engine of claim 17, wherein the afttooth is axially spaced from the cluster of teeth, the axial spacing ofthe aft tooth from the cluster of teeth being greater than 50% of theaxial length of a sealing surface of the shoe.
 19. The gas turbineengine of claim 15, further comprising a beam operatively coupling theshoe to the base.